An increasing number of wireless communication standards as applied to devices and a trend towards ever smaller, slimmer and lighter portable devices may cause major design challenges for transceiver circuitries of device. Particularly, the design challenges may relate to reduction of noise, jitters, etc. during receiving or transmission operations in the transceiver circuitry.
For example, quadrature transmitters and receivers have an inherent gain and phase imbalance between their in-phase (I) path and quadrature (Q) path. The imbalance may induce poor IMRR (Image Rejection Ratio) that may degrade overall signal to noise ratio (SNR). In this example, a previous solution to cancel the gain and phase imbalance involves a highly complex approach referred to as Asymmetric Baseband (BB) Equalizer or Complex BB Linear Adaptive Equalizer.
The solution mentioned above is based on an LMS decision directed complex BB equalizer, which includes the optimization of 4 digital filters. Given a sufficient number of coefficients for all 4 filters and for certain conditions (beyond the scope of this document), such a solution should be able to compensate for all commonly known quadrature imbalance impairments fairly well. However, this solution does not compensate for frequency-selective quadrature (IQ) gain imbalance which is not symmetrical about y-axis when plotted versus baseband-frequency (i.e., negative frequencies and positive frequencies must exhibit equal gain imbalance for the compensation filter to correct them). As such, there is a need to improve cancellation of gain and phase imbalance using a simple approach during receiving or transmitting operation in the portable device.